If you know what you're doing it isn't expensive to run a swimming pool.
This is from a member on another forum I use and the information is spot on.
I know because we have tried this method.
Quote
A walk around any pool store will have you believe that PH and Chlorine balance is all you need to do. Unfortunately this isn’t true and what the pool store isn't telling you is to their benefit. Your Cyanuric Acid (CYA) level will rise with regular use of shop bought chlorine tablets and granules because they include CYA. Your Chlorine will get used up (by the sun or by killing algae) but your CYA will not. The problem is that the more CYA you have in the water, the less effective your chlorine is at killing algae so you will have to keep going back to the shop to buy more chlorine tablets/granules (you see how this benefits them?). The excellent TFP
Trouble Free Pool forum has all you need to know (and more) but it will take some time to digest but I suggest a quick look at the Chlorine/CYA chart in the Pool School as a good starting point.
A couple of other points just for clarification:
PH+ is for raising your PH and PH- is for lowering it and you can use other chemicals to do this other than the expensive pool store products.
Bleach can be used to chlorinate your pool without raising the CYA. Yes, Bleach! You’d be surprised how alarmed people get when I tell them this until I point them to the labels and they read “Contents: Sodium Hypochlorite” on both (only use normal unscented bleach). If you haven’t got a bottle of liquid chlorine to hand, just take the lid off the bottle of bleach and have a smell, what does it smell like? The local swimming pool!
It’s a good idea to backwash when your starting pressure (where the needle is after backwashing) has gone up roughly 33% (some say 25% but I prefer 33% to save a bit of water). I’ve never been able to get my needle into the red as I think the pump would have conked out long before it got to that stage but to give you an idea. If your starting pressure is 15psi, back wash when it gets to 20 psi.
If you are serious about having the cleanest pool possible, then a professional testing kit is worth its weight in gold. I've used test strips that have told me that my CYA level was fine (between 30-50) but for some reason, I couldn't keep chlorine in the pool no matter how many times I shocked it. With my expensive (just to warn you) LaMotte FAS-DPD 7022-01 kit, it showed my CYA level to be 160! After a 75% drain and refill and SLAM (see TFP site) I now have a sparkling pool that requires very little maintenance and costs me about €1 a day, maybe even less.